On Tue 11-03-14 11:23:55, Andrew Morton wrote:
> On Wed, 19 Feb 2014 14:01:39 -0500 Tejun Heo <[email protected]> wrote:
>
> > Hello, Jan.
> >
> > On Wed, Feb 19, 2014 at 10:27:31AM +0100, Jan Kara wrote:
> > > You are the workqueue expert so you may know better ;) But the way I
> > > understand it is that queue_delayed_work() does nothing if the timer is
> > > already running. Since we queue flusher work to run either immediately or
> > > after dirty_writeback_interval we are safe to run queue_delayed_work()
> > > whenever we want it to run after dirty_writeback_interval and
> > > mod_delayed_work() whenever we want to run it immediately.
> >
> > Ah, okay, so it's always mod on immediate and queue on delayed. Yeah,
> > that should work.
> >
> > > But it's subtle and some interface where we could say queue delayed work
> > > after no later than X would be easier to grasp.
> >
> > Yeah, I think it'd be better if we had something like
> > mod_delayed_work_if_later(). Hmm...
>
> The code comments which you asked for were not forthcoming.
>
> Are you otherwise OK with merging this into 3.14 and -stable?
I have actually added the comment when nothing happened and have a patch
with Tejun's Reviewed-by. Just noone picked it up. I'll send it your way
together with another fix in flush work handling.
Honza
> From: Derek Basehore <[email protected]>
> Subject: backing_dev: fix hung task on sync
>
> bdi_wakeup_thread_delayed() used mod_delayed_work() to schedule work to
> writeback dirty inodes. The problem with this is that it can delay work
> that is scheduled for immediate execution, such as the work from
> sync_inodes_sb(). This can happen since mod_delayed_work can now steal
> work from a work_queue. This fixes the problem by using
> queue_delayed_work instead. This is a regression from the move to the bdi
> workqueue design.
>
> The reason that this causes a problem is that laptop-mode will change the
> delay, dirty_writeback_centisecs, to 60000 (10 minutes) by default. In
> the case that bdi_wakeup_thread_delayed races with sync_inodes_sb, sync
> will be stopped for 10 minutes and trigger a hung task. Even if
> dirty_writeback_centisecs is not long enough to cause a hung task, we
> still don't want to delay sync for that long.
>
> For the same reason, this also changes bdi_writeback_workfn to immediately
> queue the work again in the case that the work_list is not empty. The
> same problem can happen if the sync work is run on the rescue worker.
>
> Signed-off-by: Derek Basehore <[email protected]>
> Reviewed-by: Jan Kara <[email protected]>
> Cc: Alexander Viro <[email protected]>
> Cc: Tejun Heo <[email protected]>
> Cc: Greg Kroah-Hartman <[email protected]>
> Cc: "Darrick J. Wong" <[email protected]>
> Cc: Derek Basehore <[email protected]>
> Cc: Kees Cook <[email protected]>
> Cc: Benson Leung <[email protected]>
> Cc: Sonny Rao <[email protected]>
> Cc: Luigi Semenzato <[email protected]>
> Cc: Jens Axboe <[email protected]>
> Cc: Dave Chinner <[email protected]>
> Cc: <[email protected]>
> Signed-off-by: Andrew Morton <[email protected]>
> ---
>
> fs/fs-writeback.c | 5 +++--
> mm/backing-dev.c | 2 +-
> 2 files changed, 4 insertions(+), 3 deletions(-)
>
> diff -puN fs/fs-writeback.c~backing_dev-fix-hung-task-on-sync
> fs/fs-writeback.c
> --- a/fs/fs-writeback.c~backing_dev-fix-hung-task-on-sync
> +++ a/fs/fs-writeback.c
> @@ -1039,8 +1039,9 @@ void bdi_writeback_workfn(struct work_st
> trace_writeback_pages_written(pages_written);
> }
>
> - if (!list_empty(&bdi->work_list) ||
> - (wb_has_dirty_io(wb) && dirty_writeback_interval))
> + if (!list_empty(&bdi->work_list))
> + mod_delayed_work(bdi_wq, &wb->dwork, 0);
> + else if (wb_has_dirty_io(wb) && dirty_writeback_interval)
> queue_delayed_work(bdi_wq, &wb->dwork,
> msecs_to_jiffies(dirty_writeback_interval * 10));
>
> diff -puN mm/backing-dev.c~backing_dev-fix-hung-task-on-sync mm/backing-dev.c
> --- a/mm/backing-dev.c~backing_dev-fix-hung-task-on-sync
> +++ a/mm/backing-dev.c
> @@ -294,7 +294,7 @@ void bdi_wakeup_thread_delayed(struct ba
> unsigned long timeout;
>
> timeout = msecs_to_jiffies(dirty_writeback_interval * 10);
> - mod_delayed_work(bdi_wq, &bdi->wb.dwork, timeout);
> + queue_delayed_work(bdi_wq, &bdi->wb.dwork, timeout);
> }
>
> /*
> _
>
--
Jan Kara <[email protected]>
SUSE Labs, CR
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
